154 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



are recorded in Table II and plotted as the dotted curve of the same 

 figure, Figure 2, with one division of ordinate equal to 200 j— ^. 



TABLE II. 



If after the core of the electromagnet J has been thoroughly demag- 

 netized, a steady electromotive force E is applied to the exciting coil, 

 which consists of n turns of wire of resistance r ohms, the march of the 

 current can be predicted by the aid of equation (4). The values of 

 the slope M* (T) substituted in equation (4) permits the computation 

 of 12 (T). In a particular case with E = 10, r = 1 and n = 100, the 

 values obtained for (T) are recorded in Table III, and plotted in 

 the boundary of the shaded area of Figure 3. The actual curve which 



